The present invention relates to a slick tire that has no designs other than wear indication holes in a tread portion, and a tire building metallic mold that is used for manufacturing the slick tire. More specifically, the invention relates to a pneumatic tire capable of preventing curing failures by eliminating air accumulation, which tends to occur around a wear indication pin during building by curing, and a metallic mold used for tire building.
To build a pneumatic tire by curing, an uncured tire is inserted into a metallic mold, a diameter of the uncured tire is made to be expanded by an inner pressure to match an inner surface shape of the metallic mold and, in this state, curing is performed. In the curing process, a tread portion is lastly pressed to the inner surface of the metallic mold. For this reason, if there are no air discharging portions between the metallic mold and the uncured tire, air accumulation occurs in the tread portion, which tends to lead to a curing failure.
To deal with the above problem, various methods have been presented, such as a method of discharging air by using a vent hole or a vent groove provided inside the metallic mold, a method for discharging air from a joint of a sectional metallic mold, or the like.
However, in the case of a slick tire that has no designs in its tread portion, e.g., a racing tire, no vent holes or vent grooves like those described above have been applied for the tread portion. This is attributed to the fact that formation of a convexity in a contact patch by transfer of a vent hole or a vent groove results in lost uniformity of a contact pressure, and sufficient tire performance as a racing tire cannot be provided.
On the other hand, in the slick tire, a wear indication hole is provided in the tread portion to know a wear limit. This wear indication hole is formed by a wear indication pin, which is provided to be protruded from a tread forming surface of the metallic mold. Thus, the slick tire has had a problem that air accumulation tends to occur around the wear indication pin during building by curing. Accordingly, the air accumulation around the wear indication pin has frequently caused curing failures.
An object of the present invention is to provide a pneumatic tire, which is adapted to prevent curing failures by eliminating air accumulation around a wear indication pin during building by curing, and a metallic mold for tire building.
In order to achieve the foregoing object, a pneumatic tire of the invention, which is provided as a slick tire, includes at least one wear indication hole provided within a contact width of a tread portion thereof, wherein a distance from a shoulder contact end to the wear indication hole is set equal to 35 mm or lower, and a projected line is provided in a surface of the tread portion, the projected line having a height set in a range of 0.1 to 1.0 mm, and being extended from a position in contact with the wear indication hole to a shoulder side.
The disposition of the wear indication hole close to the shoulder and the formation of the projected line in the surface of the tread portion, the projected line being extended from the position in contact with the wear indication hole to the shoulder side, enable air to be moved through a vent groove corresponding to the projected line during building by curing and, hence, better rubber flowing can be realized. As a result, since air accumulation around a wear indication pin corresponding to the wear indication hole becomes difficult, curing failures can be prevented.
In order to achieve the foregoing object, a metallic mold for tire building of the invention is adapted to build a slick tire, which includes at least one wear indication pin within a contact width of a tread forming surface, wherein a distance from a shoulder contact end to the wear indication pin is set equal to 35 mm or lower, and a vent groove is provided in the tread forming surface, the vent groove having a depth set in a range of 0.1 to 1.0 mm, and being extended from a position in contact with the wear indication pin to a shoulder side.
The disposition of the wear indication pin close to the shoulder and the formation of the vent groove in the tread forming surface, the vent groove being extended from the position in contact with the wear indication pin to the shoulder side, enable air to be moved through the vent groove during building by curing and, hence, better rubber flowing can be realized. As a result, since air accumulation around the wear indication pin becomes difficult, curing failures can be prevented.
In accordance with the invention, if points of intersection between virtual lines in a tire meridian section are obtained for left and right shoulder portions, one of the virtual lines shaping a contour of a tread portion and being extended to the outside of a tire width direction, and the other virtual line shaping a contour of a side wall portion and being extended to the outside of a tire diameter direction, a distance between these points of intersection represents a tread width, and a contact width occupies 95% of a center of the tread width. A shoulder contact end means an end part of a shoulder side of the contact width.